Conventionally, the heat of the turbine exhaust gas in a gas turbine cycle has been recovered by the preheating of air or withdrawal of refrigerative energy by means of absorbent type refrigerant or generating of steam by a waste heat boiler. In addition, in some prior art gas turbine cycles, preheating of air is carried out through the mixture of air/steam which is obtained by injection of water into compressed air.
The following publications teach the regenerative gas turbine cycle of the water injection type; The U.S. Pat. Nos. 2,095,991, 2,115,112, 2,115,338, 2,678,532 and 2,869,324, Swiss Pat. No. 457039, and French Pat. No. 1007140.
Other publications reporting on these patents includes "GAS TURBINES WITH HEAT EXCHANGER AND WATER INJECTION IN THE COMPRESSED AIR", Combustion vol. 44, No. 6, December 1972, p. 32-40, by N. Gasparovic et al. (hereinafter referred to as report A) and Combustion vol. 45, No. 6, December 1973, p. 6-16 (hereinafter referred to as report B).
Each of the above-mentioned patents discloses the method of heat recovery by the use of a mixture of compressed air/steam with a description of the process in which injection water is mixed with the compressed air or with the intermediately compressed air. Reports A and B state in reference to these patents that the increase in thermal efficiency attainable with each of them has been proved to be about 1.5 times that for conventional simple gas turbine cycles in spite of great increase in the specific power. These achievements are not very satisfactory; rather they are poor from the viewpoint of the utility and practicability of general power generation as reflected in the concept of a combined cycle of a gas turbine and a steam turbine. With the recent skyrocketing increases in fuel prices (by 20 times in 10 years), the direction of the development of a more effective power generating plant capable of a significant increase in thermal efficiency has taken a turn toward the possibility of embodying a combined cycle of a gas turbine and steam turbine.
The applicants of the present invention have found that in the water injection type regenerative gas turbine cycle, an increase of thermal efficiency is achieved by the system in which heat recovery of turbine exhaust gas is carried out by a multi-phase mixture of compressed air/water/steam which is obtained by injection of water into a part of or the whole of compressed air and wherein intercooling of the compressor is accomplished by this water. The applicants have filed applications such as Japanese patent application No. 55-155399 on the basis of the above described discovery.
Further studies on the manner of water injection, heat recovery, and the method of production of the cooling medium have led to the additional development of the above mentioned regenerative gas turbine cycle. The improved cycle comprises contact operating means such as an exchanging tower in which direct contact between the compressed air and heated water used as a heat recovering medium occurs so that both heat and mass transfer is carried out, said liquid phase cooled water by the contact being used as a heat recovering medium for heat recovery of turbine exhaust gas and intercooling of the compressor, and wherein supplement water corresponding to the amount of water which contacts the compressed air and evaporates to transform into steam constituting the mixture is also used for intercooling of the compressor, and further cooling of the compressed air for contact operation is carried out by a part of the water which is cooled by the contact operation. This cycle has been found to achieve an increase of thermal efficiency and is presented in this invention. It has also been proved that the values of thermal efficiency obtainable by this cycle are higher in comparison with those expected for the above mentioned combined reheat cycle of a gas turbine and a steam turbine.